EGU General Assembly Vienna AT 9 April 2018

EGU General Assembly, Vienna, AT, 9 April 2018 A review of methods to estimate regional and global glacier mass balances Michael Zemp, Laura Thomson, Emmanuel Thibert, Frank Paul, Samuel U. Nussbaumer, Robert Mc. Nabb, Fabien Maussion, Horst Machguth, Matthias Huss, Jacqueline Huber, Isabelle Gärtner-Roer, Nicolas Eckert, and Martina Barandun March 2018 @ Ibergeregg, CH

How best assess regional mass balance from few observation series? The Alps Kääb et al. (2013) Photo: M. Zemp

review AR 4 and AR 5 methods Pleiades, CNES Airbus Graphic: P. Joerg ¦ Cryosat-2, ESA new method ¦ preliminary results Tan. DEM-X, DLR

review AR 4 and AR 5 methods ¦ new method ¦ preliminary results Mass balance estimates in past IPCC Reports IPCC WGI AR 5 (2013) Gardner et al. (2013) § glac. and geod. estimates based on: Cogley (2009) § arithmetic mean of glac. balances § spatial interpolation of glac. balances at 1°x 1°grid § spatial interpolation of glac. and geod. balances at 1°x 1°grid IPCC WGI AR 4 (2007) Kaser et al. (2013) § glac. estimates based on: § Cogely (2005): arithmetic averaging and polynomial spatial interpolation § Dyurgerov & Meier (2005), Ohmura (2004): area-weighting => Time resolution: pentades

review AR 4 and AR 5 methods ¦ new method ¦ preliminary results Review methods used in AR 4 and AR 5 in sandbox experiment

review AR 4 and AR 5 methods ¦ new method ¦ preliminary results Method evaluation in the Swiss “sandbox”: B. geodetic Time period: 1980 -2010 No. of glaciers: 1385 S 1980: 1255 km 2 S 2010: 948 km 2 Savg: 1102 km 2 ρ: 850 kg m-3 + increasing number of observations + representative samples allow for validation & calibration over longer periods Sum of Bgeod: -19. 13 Gt - common time periods - completeness of inventory - area changes - density conversion “Arithmetic Mean of Geodetic Balances”: -15 Gt Strong underestimation when calculating Bgeod from d. Vavg and Savg! Fischer et al. (2014, 2015)

review AR 4 and AR 5 methods ¦ new method ¦ preliminary results B. glac using arithmetic mean Time period: 1980/81 -2009/10 No. of glaciers: 4 Savg: 1102 km 2 Bglac. cum: -18. 8 m w. e. Bglac. cum: -20. 7 Gt + simple & fast method + few information required - very sensitive to sample - changing sample over time

review AR 4 and AR 5 methods ¦ new method ¦ preliminary results B. glac using arithmetic mean at 1° x 1° grid Time period: 1980/81 -2009/10 No. of glaciers: 4 Savg: 1102 km 2 Bglac. cum: -18. 8 m w. e. Bavg. centerpoints: -18. 7 m w. e. Bglac. cum: -20. 6 Gt

review AR 4 and AR 5 methods ¦ new method ¦ preliminary results B. glac using area-weigthed mean at 1° x 1° grid Time period: 1980/81 -2009/10 No. of glaciers: 4 Savg: 1102 km 2 Bglac. cum: -18. 7 Gt

review AR 4 and AR 5 methods ¦ new method ¦ preliminary results B. glac interpolated to inventory points multiplied with indv. S Time period: 1980/81 -2009/10 No. of glaciers: 4 / 1385 Savg: 1102 km 2 Bglac. cum: -20. 1 Gt + regional climatic variability + glacier distribution in space - ignores effect of hypsography - extrapolation of absolute Ba values

review AR 4 and AR 5 methods ¦ new method ¦ preliminary results Swiss balance estimates 1980 -2010 in comparison excluding GRIES? ? ? Approach Bcum Gt Δ ref B. geod, sum of all glaciers -19. 1 ref B. geod, arithmetic mean multiplied with surface area -15. 0 +21. 5% B. glac, arithmetic mean -20. 7 -8. 4% B. glac, arithmetic mean at 1° x 1° grid -20. 6 -7. 9% B. glac, area-weighted mean at 1° x 1° grid -18. 7 +2. 1% B. glac, interpolated to glacier locations, multiplied with indv. S -20. 1 -5. 2%

review AR 4 and AR 5 methods ¦ new method ¦ preliminary results Swiss balance estimates 1980 -2010 in comparison excluding GRIES!!! Approach Bcum Gt Δ ref B. geod, sum of all glaciers -19. 1 ref B. geod, arithmetic mean multiplied with surface area -15. 0 +21. 5% B. glac, arithmetic mean -16. 0 +16. 2% B. glac, arithmetic mean at 1° x 1° grid -16. 0 +16. 2% B. glac, area-weighted mean at 1° x 1° grid -15. 3 +19. 9% B. glac, interpolated to glacier locations, multiplied with indv. S -13. 3 +30. 4%

review AR 4 and AR 5 methods ¦ new method ¦ preliminary results Swiss balance estimates 1980 -2010 in comparison Combine the temporal variability of the glaciological with the absolute value of the geodetic balance! cf. Zemp et al. 2013, The Cryosphere fotomelia. com

review AR 4 and AR 5 methods ¦ new method ¦ preliminary results Temporal signal: variance analysis of glac. data building on Lliboutry’s linear model J. Glaciol. 1974

review AR 4 and AR 5 methods ¦ new method ¦ preliminary results Temporal signal: variance analysis of glac. data

review AR 4 and AR 5 methods ¦ new method ¦ preliminary results Absolute value: calibrate glaciological with geodetic

review AR 4 and AR 5 methods ¦ new method ¦ preliminary results avg diff. to Gardner et al. (2013) Very preliminary results for 2003 -2009 arithm. avg ¦ area-weighted avg ¦ interpolated to RGI glaciers ¦ Gardner et al. (2013)

review AR 4 and AR 5 methods ¦ new method ¦ preliminary results Thanks for your attention! sw r. d e SROCC Kahlitna Glacier, Alaska, from www. swisseduc. ch/glaciers/